The present invention relates to a technology for identifying a person using a living body, and more particularly to a technology for identifying a person using a finger vein pattern.
Today, the typical personal identification technology is fingerprint identification. However, the problem is that other person""s fingerprint is easily obtained, for example, a criminal""s fingerprint is taken in the scene of a crime, and therefore a finger-print may be forged. This problem leads to the development of personal identification technologies other than fingerprint identification. For example, JP-A-7-21373, laid-open Jan. 24, 1995, discloses a personal identification technology thorough the use of a finger blood vessel pattern, and JP-A-10-295674, laid-open Nov. 10, 1998, discloses a personal identification technology through the use of a vein pattern on the back of a hand. These technologies shine a light on a finger or on the back of a hand, capture the reflected light or transmitted light, extract the blood vessel pattern from the captured image, and compare the captured blood vessel pattern with the previously-registered blood vessel pattern to identify a person.
However, there are some problems in implementing a personal identification system that uses finger vein patterns.
One of the problems is the reproducibility of a captured image. Although a conventional personal identification system has positioning parts such as a pin or a grasping bar for stabilizing the imaging region, an error in the imaging region is unavoidable, for example, when a finger is rotated or moved in the plane or when a finger is rotated on its major axis. Therefore, it is difficult to completely match a registered vein pattern with a vein pattern obtained at identification time, with the result that the performance of identification is reduced. In particular, on a fully-non-contact system on which the finger is not put on something for fixing, a registered vein pattern and a captured vein pattern may differ largely and this difference further reduces the performance of identification.
Another problem is a light source. A conventional personal identification system has no function to adjust the amount of light from the light source. This generates several image-quality problems such as a blurred outline of a captured image, a lack in sharpness, and a low contrast. These problems require a complex image-processing algorithm for correction and sometimes result in the low performance of identification.
According to one aspect of the present invention, means described below is used for improving reproducibility. First means is an algorithm for correcting an error detected during image processing that is executed for matching an imaged finger blood vessel pattern with a registered pattern. This correction prevents the performance of identification from being degraded.
Second means is a three-dimensional imaging of a living body from various angles using a plurality of imaging devices. Even if a registered vein pattern was imaged from only one direction, that is, the registered pattern is two-dimensional data, the finger may be placed freely when imaged for identification. Therefore, even if there is an error in the imaging region, one of the plurality of images may be selected for use in matching. This prevents the performance of identification from being degraded. It is also possible to register three-dimensional vein patterns as patterns to be registered by imaging the vein pattern from a plurality of directions. In this case, one of the plurality of registered vein patterns is selected for matching. This also prevents the performance of identification from being degraded even if there is an error in the imaging region.
Combining the first means with the second means further increases the performance of identification.
A light source with means for optimizing the amount of light at imaging time is used as the light source. This configuration optimizes the amount of light from the light source to make the quality of a captured image best.